Most automatic transmissions for shifting gears in automobile engines comprise various sun and planetary gears with appropriate clutch plates and bands responsive to hydraulic oil pressure to hold one or more gears and thus change the effective ratio between input shaft speed from the engine and output shaft speed to the wheels. The heart of such transmission systems is a valve body and casing containing various inter-related passages, valves, springs and orifices. The valve body receives signals in the form of hydraulic pressures which function to shift various ones of the shift valves to thereby route the transmission oil through appropriate passages in the casing to clutch plates and bands (referred to as "apply units") and thus automatically effect sequential shifting within a given range. The referred-to signals in the form of hydraulic pressure are functions of the transmission shaft speed and torque.
The valve body itself cooperates with a separator plate normally positioned between the valve body and casing. This separator plate includes various sized and positioned orifices and openings communicating with various ones of the inter-related passages in the valve body and casing so as to route oil between the passages as well as through the passages to apply units. Essentially, this separator plate in cooperation with the valve body and casing "tells" the transmission when to shift and how to shift.
Stock or standard automatic transmissions effect shifting in a relatively "gradual" manner; that is, the shifting is calibrated to provide a relatively smooth acceleration when shifting from one gear to a next higher gear to thereby minimize "jerking".
While such type shifting is primarily provided for the comfort of the average driver, it exhibits a distinct disadvantage. More particularly, there results an extended slippage time between the clutch plates and bands which prevents the inertial energy from being effectively utilized. This energy is simply lost in the form of heat on the clutches and bands instead of being utilized for forward motion. As a result, continually operating a stock or standard automatic transmission at full throttle will cause early friction element failure.
In order to realize high performance and improve durability in an automatic transmission, the shifting must be recalibrated to precisely control the relatively complicated chain of events that occurs during every shift and must accomplish such control in a substantially briefer period or span of time. Actually, if the period of time between the start of a shift and its completion can be reduced, the overall life of the transmission is substantially increased.
Normally, to recalibrate a transmission system requires disassembly of many components including in many instances some of the sun and planetary gear structures themselves in the transmission. As an example, in certain concentric or coaxial gear assemblies it is possible to remove a sealing O-ring in order to effectively increase the area upon which transmission oil pressure acts in operating clutch plates or clutch bands. Access must thus be had to the main body of the transmission system. It would be desirable if there were some convenient means of simply recalibrating the valve body itself which is more readily accessible rather than require disassembly of the transmission gear system.